In its 2013 publication of “NFPA 13: Standard for the Installation of Sprinkler Systems” (herein after “NFPA 13”), the National Fire Protection Association (NFPA) defines an automatic sprinkler as “a fire suppression or control device that operates automatically when its heat-activated element is heated to its thermal rating or above, allowing water to discharge over a specified area.” A known heat-activated element for use in an automatic sprinkler is a thermally responsive frangible bulb, as seen for example, in U.S. Pat. No. 5,967,238. An automatic sprinkler can be characterized by the physical dimensions and thermal characteristics, i.e., nominal temperature rating and Response Time Index (RTI), of its thermally responsive bulb. U.S. Pat. No. 5,967,238 describes a thermally responsive frangible bulb with a maximum bulb diameter of about 0.1 inch and a maximum bulb length of less than 1 inch. Other known thermally responsive bulbs are manufactured with a maximum length of more than ¾ inch, a maximum RTI of 90 meter1/2 sec1/2 (m1/2s1/2) and a nominal temperature rating defined under NFPA 13 being any one of: (i) ordinary 135° F.-170° F.; (ii) intermediate 175° F.-225° F.; (iii) high 250° F.-300° F.; (iv) extra high 325° F.-375° F.; (v) very extra high 400° F.-475° F.; and (vi) ultra high 500° F.-575° F.
In addition to its thermally responsive bulb, an automatic sprinkler can also be characterized by its discharge characteristics. A sprinkler's discharge characteristics can be identified by a nominal K-factor which is defined as an average flow of water in gallons per minute through the internal passageway divided by a square root of pressure of water fed into the inlet end of the internal passageway in pounds per square inch gauge: Q=K√P where P represents the pressure of water fed into the inlet end of the internal passageway through the body of the sprinkler, in pounds per square inch gauge (psig); Q represents the flow of water from the outlet end of the internal passageway through the body of the sprinkler, in gallons per minute (gpm); and K represents the nominal K-factor constant in units of gallons per minute divided by the square root of pressure expressed in psig. Known nominal K-factors include (with the K-factor range shown in parenthesis): (i) 14.0 (13.5-14.5) GPM/(PSI)1/2; (ii) 16.8 (16.0-17.6) GPM/(PSI)1/2; (iii) 19.6 (18.6-20.6) GPM/(PSI)1/2; (iv) 22.4 (21.3-23.5) GPM/(PSI)1/2; (v) 25.2 (23.9-26.5) GPM/(PSI)1/2; (vi) 28.0 (26.6-29.4) GPM/(PSI)1/2; and (vii) 33.6 (31.9-35.28) GPM/(PSI)½.
For automatic sprinklers with a nominal K-factor of 16 GPM/(PSI)1/2 and larger, the heat-activated element might be a strut and lever arrangement with a thermally responsive solder element. U.S. Pat. Nos. 5,609,211; 8,602,118; and 8,408,321 and U.S. Patent Publication No. 20080073088 generally show and describe sprinklers with a thermally actuated bulb with a nominal K-factor of 25.2 GPM/(PSI)1/2 or larger. Although these patents, for example U.S. Pat. No. 8,408,321, indicate that sprinklers having a nominal K-factor larger than 25.2 GPM/(PSI)1/2 with a bulb-type trigger are applicable for the described dry-pipe sprinkler system, the patent does not describe any particular details of the glass bulb, bulb seating and/or applications for combining a sprinkler with a K-factor greater than 25.2 GPM/(PSI)1/2 with a glass bulb.